Why QFileDialog::selectFile doesn't work?

Question

I am using Qt 5.12 and trying to write test (using QTest) for opening of project stored in some xml format.

In test I use QTimer::singleShot to wait QFileDialog to appear as proposed in QT close window by QTest in locked thread.

The problem is that QFileDialog::selectFile doesn't select anything. This means that OK button is not active, so I can't click on it in my test.

I assume in the following example that full path to file is /tmp/project.xml. Notice that QFileDialog::setDirectory works great: when the following example starts, you are in /tmp dir instead of /.

#include <QApplication>

#include <QFileDialog>
#include <QTimer>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QTimer::singleShot(300, []() {
        QWidget* window = nullptr;
        while (!window) {
            window = qApp->activeModalWidget();
        }
        QFileDialog* fd = qobject_cast<QFileDialog*>(window);

        fd->setDirectory("/tmp");
        fd->selectFile("project.xml");
    });

    QString path = QFileDialog::getOpenFileName(nullptr, "Open Project",
                                                "/", QString(),
                                                nullptr, QFileDialog::DontUseNativeDialog);
}

Answer 1

The function selectFile didn't work because of the file name text box (lineEdit) is focused. This behavior comes from the implementation of QFileDialog::selectFile() :

void QFileDialog::selectFile(const QString &filename)
{
    // ... function body

    //Put the filename into the lineEdit when :
    //1. The dialog is not visible or
    //2. The lineEdit is not focused.

    if (!isVisible() || !d->lineEdit()->hasFocus())
        d->lineEdit()->setText(index.isValid() ? index.data().toString() : fileFromPath(d->rootPath(), filename));
}

To make the program works, there are two ways :

1. Put the file name directly in the text box

2. Give the focus away then call selectFile

      fd->setDirectory("/tmp");
   
      QLineEdit * lineEdit = qobject_cast<QLineEdit*>(fd->focusWidget());
   
       if( lineEdit ){
   
           //Method 1
           lineEdit->setText("project.xml");
   
           //Method 2
           lineEdit->nextInFocusChain()->setFocus();
           fd->selectFile("project.xml");
   
       }else { //no lineEdit focus found
   
           fd->selectFile("project.xml");
       }